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Some knowledge of basic marine electrics and boat wiring is useful for all boat skippers. It is essential for skippers wanting to establish self-sufficiency or those planning to be responsible for maintaining or restoring their boat. This note develops a few introductory points.
Smaller commercial vessels and recreational yachts are usually fitted with 12 or 24 volt direct current (DC) electricity systems. The cabling for these systems is typically configured as a two-wire, one pole insulated and grounded scheme. Based on this cabling design, all electrical devices are connected onboard the vessel with one negative plus one positive wire.
In a two wire system, both the positive and negative supply circuit have a double pole short circuit protection plus an isolation device installed. These are usually placed within a single, trip free circuit breaker. The isolator must be designed consistent with the maximum current to be carried by the circuit.
The cabling is stranded wire rather than solid wire. Solid wire is not used since it is tends to be open to to breakage due to persistent vibration. However, if stranded wire is too fine, it can easily break and is also prone to corrosion. Consequently, 16 gauge wire is commonly recommended as a minimum thickness with thicker wire used depending on the amount of current load.
The insulation material used to coat the cabling should be rated as both moisture resistant and flame retarding. Insulation for cabling in the engine and bilge areas should additionally be oil resistant. Split, frayed or cracked insulation should be promptly replaced. The engine and bilge areas generate difficult environments that can erode insulation with time so regular inspections are appropriate.
If it is possible, electric cabling should not be routed through the bilge. However, where that is not possible, it should be placed high in the bilge to avoid water contact. Similarly, cabling should not be run through compartments or areas that contain systems that may discharge corrosive emissions.
Cabling should be installed without kinks or sharp ends that might promote metal fatigue and wiring fracture. Similarly, cabling should be fixed so that it does not flex or move with vessel vibrations. To conform with this requirement, wiring is supported at intervals of no greater than 18 inches (45 centimeters).
Similarly, boat wiring should be protected from chafing at points where it passes through holes such as at bulkheads and junction boxes. A minimum of splices should be used and where they are must be made they should be soldered and sealed from moisture.
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